Apparatus for trimming electrical resistors

ABSTRACT

An apparatus for guiding the powdered abrasive cutting nozzle upon a micro-electronic circuit board to decrease the cross sectional area of an electrical conducting strip thereon, the apparatus employing a variable speed linkage assembly to effect movement of the circuit board into association with the abrasive cutting nozzle, an electrical circuit connected through a probe assembly to measure the electrical resistance of the trimmed conducting strip upon the circuit board, the probe assembly being movable between a conducting position and a nonconducting position.

United States Patent Lambert is] 3,685,209 51 Aug. 22, 1972 154] APPARATUS FOR TRIMMING ELECTRICAL RESISTORS [72] Inventor: Arthur H. Lambert, Los Angeles,

Calif.

[73] Assignee: Comco Supply, lnc., Burbank, Calif. [22] Filed: Aug. 20, 1970 [21] Appl. No.: 65,601

[52]. US. Cl ..51/14, 51/165.14

[51] Int. Cl ..B24c 3/04 [58] Field ofSearch ..51/8,12,14,l5,95 LH, 51/319,320,165.74

[56] References Cited UNITED STATES PATENTS 2,743,554 5/1956 Daileyet a1 ..51/15 2,773,332 12/1956 Buchman et al ..51/15 2,884,746 5/1959 Rus et a1. ..5 H50 R X 3,425,166 2/1969 Best et al ..51/14 3,516,204 6/1970 Kulischenko ..5 H8 3,534,503 10/1970 Kulischenko ..5 l/ 8 Primary Examiner-Lester M. Swingle Att0rneyRobert E. Geauque [57] ABSTRACT An apparatus for guiding the powdered abrasive cutting nozzle upon 'a micro-electronic circuit board to decrease the cross sectional area of an electrical conducting strip thereon, the apparatus employing a variable speed linkage assembly to effect movement of the circuit board into association with the abrasive cutting nozzle, an electrical circuit connected through a probe assembly to measure the electrical resistance of the trimmed conducting strip upon the circuit board, the probe assembly being movable between a conducting position and a nonconducting position.

4 Claim, 6 Drawing Figures PATENTED MIR 2 2 I972 SHEET 3 [IF 3 I60 4/97/40 A. ZAMBEFT INYENTOR. I

BY 4770 PA/KV APPARATUS FOR TRIMMING ELECTRICAL RESISTORS BACKGROUND OF THE INVENTION The field of this invention relates to abrasive cutting tools and more particularly to an abrasive cutting tool which employs the use of an extremely fine particulate abrasive powder to effect accurate trimming of electrical resistors.

The apparatus of this invention is to be employed in conjunction with an apparatus for dispensing abrasive powder such as shown and described in US. Pat. application, Ser. No. 842,881, filed July 18, 1969, entitled APPARATUS FOR DISPENSING POWDER SUCH AS AN ABRASIVE POWDER, by Herbert G. Weightman, now US. Pat. No. 3,638,839, dated Feb. 1, 1972.

The abrasive powder dispenser of the aforementioned patent application causes a mixing of the abrasive powder with pressurized air, the air causing the abrasive powder to be carried to a nozzle from which the abrasive ladencd air is discharged in the form of a high velocity abrasive cutting jet. Abrasive cutting tools of this type are employed for a variety of precision operations such as finishing surfaces, removing burrs, removing surface coatings, trimming electrical resistors, and other uses. In the designing of electrical equipment which performs a multitude of functions, a great amount of complex circuitry must be employed to effect the desired functions. Circuits which are formed by use of conventional conducting wires, resistors, conductors and capacitors take up a substantial amount of space in forming complex circuitry. In electrical equipment which are designed to perform a multitude of functions (such as computers), to avoid such from becoming extremely immense in size, an effort has been made in recent years to produce circuitry which can perform the same number of functions but which is substantially smaller in physical size.

In recent years a space saving circuitry assembly has been commercially available and is commonly referred to broadly as micro-electronics. The circuitsformed within the field of micro-electronics are extremely small and are normally emobssed upon a thin wafer like circuit board. Within a single circuit board of approxitrical resistance of each of the circuits of each of the conducting circuits within the circuit board. In the past this has been found to be extremely difficult to accomplish. The easiest procedure to accomplish such a change in resistance has been to physically trim each of the conducting strips by means of decreasing the width of the strip, thereby automatically decreasing the conducting area. One way in which this can be accomplished is by placing a resistance measuring meter in circuit with the strip and physically decrease the width of the strip until the desired resistance value of the strip is measured by the meter. However, for such a procedure to be accomplished manually, it is normally not possible for a human being to accurately trim a conducting strip the exact amount necessary to achieve the degree of accuracy necessary. Further, such a procedure becomes tedious as usually a large number of circuit boards must be trimmed.

In an effort to produce a large number of circuit boards, each having circuitry identical to each other, and each of the conducting strips within each of the circuit boards having accurately measured electrical resistance, it has been common to employ an automatic trimming apparatus. Normally such previous automatic trimming apparatuses caused movement of the abrasive cutting nozzle into the circuit board and into the particular conducting strip in which it is desired to decrease the electrical resistance therein. It is normally common to employ the use of an electrical bridge balancing structure which measures the electrical resistance and then automatically shuts off the trimming apparatus upon the desired resistance having been achieved as measured by the electrical bridge.

Although such an apparatus has completely eliminated any skill on the part of the operator in effecting the trimming, such apparatus has proved to be undesirable. For example, it has been found that during the short interval of time that the bridge is balanced, indicating the achieving of the desired electrical resistance and the cut-off of the apparatus occurring, a small amount of continual cutting action occurs which produces a certain amount of inaccuracy. Also, such automatic trimming apparatuses are normally substantially complex in construction and thereby being substantially expensive to manufacture. Further, such automatic apparatuses have not been able to move quickly into and out of position while yet permitting extremely fine increment movement of the conducting strip into direct association with the cutting nozzle. Normally, such automatic trimming apparatuses change the speed of the driving motor which drives or effects movement of the cutting nozzle. Such changing of the speed of the driving motor inherently is not capable of extremely accurate adjustment as to increments of movement.

SUMMARY OF THE INVENTION The trimming apparatus of this invention to effect an extremely accurate trimming operating causes the circuit board to move into and out of associated with a fixedly located cutting nozzle. A human operator visually determines the extent of the cutting operation and causes movement of the circuit board out of association with the cutting nozzle. As a result of employing the use of a human operator, a substantially greater degree of accuracy is achieved that was heretofore not possible. The circuit board is moved at very fine increments when closely located with respect to the cutting nozzle. Also, the circuit board is moved in substantially larger increments when displaced a short distance away from the cutting nozzle.

The trimming apparatus of this invention employs the use of a fixedly located head to which is to be positioned thereon a nozzle through which an abrasive cutting powder is to be conducted. A micro-electronic circuit board is to be fixedly located upon an intermediate supporting base which is to be movable with respect to a fixed base toward and away from the cutting nozzle. The intermediate base is to be manually moved through a linkage assembly with respect to the fixed base. The linkage assembly permits variable speed movement of the circuit board with respect to the nozzle, large distance movement when not in close proximity to the cutting nozzle and extremely small increment movement when the circuit board is in close proximity to the cutting nozzle. A probe assembly is to be located adjacent to the circuit board and positionable to establish an electrical connection with a particular electrically conducting strip upon the circuit board. The probe assembly is adapted to be moved to a noninterfering position with respect to the circuit board when the circuit board is in the maximum displaced position from the cutting nozzle. A balancing bridge meter assembly is electrically connected with respect to the probe assembly.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view of the trimming apparatus of this invention;

FIG. 2 is a right side view of the trimming apparatus of this invention shown in FIG. 1;

FIG. 3 is a partly-in-section top view of the trimming apparatus of this invention taken along line 3-3 of FIG. 2;

FIG. 4 is a sectional view along the trimming apparatus of this invention taken along line 44 of FIG. 3;

FIG. 5 is a partly-in-section bottom view taken along line 55 of FIG. 2 showing in more detail the linkage assembly employed within this invention; and

FIG. 6 is a sectional view taken along line 6-6 of FIG. 5 showing in more detail portions of the linkage apparatus employed within this invention.

DETAILED DESCRIPTION OF THE SHOWN EMBODIMENT Referring particularly to the drawings, there is shown in FIG. 1 the apparatus 10 of this invention being composed generally of a fixed base 12, an intermediate base 14, a head portion 16 and a back section 18. A nozzle 20 is fixedly secured within the head portion 16 and is adapted to transmit therethrough finely particulated abrasive material combined with air from a source (not shown). The head portion 16 is pivotally mounted by pivot pin 22 to the back section 18. Head portion 16 has a hollow central chamber 24, the function of which will be explained further on in this specification. A sleeve 26 is fixedly secured exteriorly about head portion 16 in the area of the pivot pin 22. Secured to sleeve 26 is a first lug 28 and a second lug 30. First lug 28 is located on the opposite side of sleeve 26 with respect to second lug 30. F ixedly retained within an aperture within the first lug 28 is a nut 32. Nut 32 cooperates with a threaded bolt 34 which extends exteriorlyof back section 18 through an aperture 36. Rounded head 38 which is integrally connected to bolt 34 prevents disassociation of bolt 34 from aperture 36. A knurled knob 40 is secured to rounded head 38 and facilitates manual rotation of bolt 34. A compression spring 42 is located between back section 18 and first lug 28. It is to be noted that upon rotation of bolt 34, pivoting movement of head 16 with respect to back section 18 occurs about pivot pin 22.

Second lug 30 functions as a guide to permit sliding movement of bolt 34 which is threadingly secured to third lug 46. Third lug 46 is fixedly secured to head l6.

A portion of bolt 44 extends exteriorly of back section 18 through a slot 48. A knurled knob 50 is secured to bolt 44 and prevents disassociation of bolt 44 from slot 48 within the back section 18. It is the function of bolts 44 and 34 to permit angular adjustment of the head 16 with respect to the back section 18 as will be explained further on in this specification.

A vacuum from a source (not shown) is to be applied through conduit 52 into chamber 24. The vacuum is to effect removal of the abrasive particulates which have been conducted through nozzle 20 after such had been used to avoid the particulates from entering into the atmosphere and form a layer of dust upon the apparatus 10.

Intermediate base 14 includes a main supporting plate 54 to which are secured a fore plate 56 and an aft plate 58. Side plates 60 are also secured between fore plate 56 and aft plate 58 on the lateral sides of main supporting plate 54, thereby forming a substantially enclosed chamber 62. Between the fore plate 56 and the aft plate 58 are fixedly secured a pair of spaced apart rods 64 and 66. Rod 64 cooperates interiorly with a guide mechanism 68 with rod 66 cooperating in a similar manner with a guide mechanism 70. Each of the guide mechanisms 68 and 70 are fixedly secured to fixed base 12. Also, each of the guide mechanisms 68 and 70 are identical in construction and include bearings 72 to effect extremely accurate longitudinal movement of the intermediate base 14 with respect to the fixed base 12.

Fixedly secured by set screw 74 to fore plate 56 is a rod 76. Rod 76 passes through slot 78 formed within fixed base 12 and is secured to block 80 which is capable of limited sliding movement within groove 82 of bifurcated arm 84. The free end of bifurcated arm 84 is pivotally secured through pivot pin 86 to plate 88. Plate 88 is pivotally attached by pivot pin 90 to fixed base 12.

Intermediate the ends of bifurcated arm 84 is pivotally secured by pivot pin 92 a linkage arm 94. An actuating arm 96 is pivotally secured to the free end of linkage arm 94 through pivot pin 98 and also pivotally secured through pivot pin 100 to plate 88. Actuating arm 96 passes through a slot 102 formed within the fixed base 12. An enlarged knob 104 is fixedly secured to the free end of actuating arm 96.

Intermediate base 14 also includes a lower housing 106 and an upper housing 108. Housing 106 is fixedly secured upon main supporting plate 54. Upper housing 108 is secured to lower housing 106 with platform 110 being mounted upon upper housing 108. Platform 110 is movable with respect to upper housing 108 by means of a mechanism (not shown). The mechanism to effect such movement is conventional and need not be described here in detail. An adjusting knob 112 is provided through upper housing 108 to effect the aforesaid adjustment.

To be fixedly positioned by restraining means (not shown) upon platform 110 is circuit board 114. Circuit board 114 is to also be of conventional design and have a plurality of electrically conducting strips formed thereon (not shown).

Rotatably secured with respect to lower housing 106 by means of shaft 116 are first and second flange plates 118 and 120, respectively. A weight 166 is secured through fixed shaft 168 to flange plate 118. Secured to the upper surface of flange plate 118 is a supporting plate 122, and in a similar manner secured to the upper edge of flange plate 120 is a supporting plate 124. Pivotally secured to supporting plate 122 is a trunnion 126 and also pivotally secured to supporting plate 124 is trunnion 128. A bolt 130 is threadingly associated with trunnion 126. In a'similar manner a bolt 132 is threadingly associated with trunnion 128. A knurled knob 134 is attached to bolt 130 with a knurled knob 136 being attached to bolt 132. A probe 138 is secured to bolt 130 at the free end thereof and in a similar manner a probe 140 is connected to bolt 132 at the free end thereof. Each of the probes 138 and 140, upon the establishment of an electrically conductive element therebetween, is capable of establishing an electrical circuit through conducting strips (not shown) of the circuit board 114. The value of the resistance of the conducting strips is to be visually observed by meter 142. Located within the circuit between the probes 138 and 140 and the meter 142 is a conventional electrical bridge circuit which is commonly referred to as a balancing bridge. This bridge circuit is capable of adjustment so that upon a particular electrical resistance being placed between the probes 138 and 140 the meter 142 will register at a numerical value of zero, thereby indicating a balancing of the circuit has been achieved.

Secured to shaft 16 interiorly of lower housing 106 is a dog 144. A follower rod 146 is conducted through an aperture in the main supporting plate 54 and in contactual relationship with dog 144. A stop washer 148 is secured to follower rod 146 to limit the amount of downward movement of follower rod 146. A second washer 150 is secured to follower rod 146, with a spring 152 being located between washer 150 and main supporting plate 54. Spring 152 functions to tend to maintain follower rod 146 in the lower position with stop washer 148 in contactual relationship with main supporting plate 54.

The free end of follower rod 146 is to be contactable with the forward end of a pivoting arm 154. Arm 154 is pivotally secured through pivot pin 156 to fixed base 12. The aft end of pivoting arm 154 comprises a cam surface 158. A follower 160 is adapted to be in continuous contactual relationship with cam surface 158. Follower 160 is secured to the piston of a conventional piston and cylinder 162. The cylinder of the piston and cylinder 162 is fixedly connected to the base 12. Activation of the piston and cylinder 162 is caused by a switching mechanism (not shown) at the option of the human operator.

The operation of the apparatus of this invention is as follows: With the intermediate base 14 in the furtherest displaced position from back section 18, follower 160 is moved up cam surface 158 causing pivoting arm 154 to be pivoted against follower rod 146. Spring 152 is compressed and shaft 116 is rotated due to the force exerted by follower rod 146 against dog 144. The probes 138 and 140 which are connected to shaft 116 are caused to assume a displaced position from platform 110 as shown in F IG. 6 of the drawings. This position facilitates the placement by an operator of a circuit board 114 upon platform 110. The operator then grasps enlarged knob 104 of actuating arm 96 and then proceeds to effect movement of arm 96. The probes 138 and then fall by gravity upon the circuit board 114. A positive electrical contact is insured due to weight 166. During movement of the arm 96 from the distance A as shown in FIG. 5 of the drawings the particular conducting strip which is desired to be trimmed that is located upon the circuit board 114 is moved directly adjacent the nozzle 20. Bifurcated arm 84 has been pivoted until such is in an abutting relationship with plate 88. It is to be understood that the position of nozzle 20 has been predetermined by rotating knurled knobs 40 and 50, which in turn effect rotation of their respective bolts 34 and 44. Rotation of bolt 34 in one direction causes head 16, which contains nozzle 20, to be pivoted in the counter clockwise direction as shown in FIG. 3 of the drawings. Rotation of bolt 34 in the opposite direction likewise causes pivoting of head 16 in the clockwise direction. Bolt 44 permits longitudinal adjustment of the head 16 with respect to the back section 18.

With the particular conducting strip of the circuit board 114 in' very close proximity to nozzle 20 the operator then proceeds to move knob 104 the distance B as shown in F IG. 5 of the drawings. The operator may or may not move the knob 104 the entire distance B. It is to be noted that B is a greater distance than distance A. However, because bifurcated arm 84 is in abutting contact with plate 88, plate 88 begins to pivot about pivot pin 90. Because rod 76 which effects a movement of the intermediate base 14 is only a relatively short distance from pivot pin 90, the intermediate base 14 moves only a very short distance although distance B is quite large. Also, when bifurcated arm 84 comes into contact with plate 88 a microswitch (not shown) is activated which activates the powdered abrasive being conducted through nozzle 20 and also the vacuum within the chamber 24. As the operator moves the knob 104 along the distance B, the powdered abrasive being conducted through nozzle 20 is causing a decrease in width of a specific conducting strip upon circuit board 114. The probes 138 and 140 which are located on each end of the particular conducting strip are causing an electrical circuit to be established within the particular conducting strip. This electrical circuit is a portion of a balancing bridge which in essence compares the electrical resistance of the conducting strip and records such for visual observance upon meter 142. Upon the particular conducting strip being trimmed sufficiently to the value of the resistance desired, the meter 142 will register a value of zero indicating to the operator that the desired value of resistance has been achieved. The operator then pulls backward on knob 104 removing the circuit board 1 14 out of association with nozzle 20. It is to be noted that spring 164 assists in such movement by tending to pivot plate 88 toward the solid position shown in FIG. 5 of the drawings. As the operator continues to move knob 104 in the backward direction along direction A, upon bifurcated arm 84 being removed from in contactual relationship with plate 88 a microswitch (not shown) is deactivated which deactivates the powdered abrasive passing through nozzle 20 and also deactivates the vacuum within chamber 24. Upon the knob 104 reaching the rearwardmost position the probes 138 and 140 are pivoted by activation of a switch (not shown) by the operator up and away from the circuit board 114. The operator can then easily remove the trim circuit board 114 from the platform 110 and replace it with a similar circuit board 114 which is untrimmed. The procedure is again repeated for the untrimmed circuit board 114.

What is claimed is: 1. An electrical resistor trimming apparatus comprising:

first means for decreasing the cross sectional area of an electrical resistor; second means for fixedly locating the electrical resistor on a support; third means for moving the electrical resistor into and out of association with said first means, said third means including variable speed structure to move the support and the electrical resistor at different velocities. 2. An electrical resistor trimming apparatus comprismg:

first means for decreasing the cross sectional area of an electrical resistor; second means for fixedly locating the electrical re sistor on a support; third means for moving the support and the electrical resistor into and out of association with said first means, said third means including variable speed structure; and said variable speed structure includes an actuating arm movable by an actuating force, said actuating arm connected to actuate a first linkage arm and a second linkage arm, said first linkage arm movable with respect to said second linkage arm and causing the electrical resistor to move a first distance toward said first means, said second linkage arm movable subsequent to the completion of movement of said first linkage arm, said second linkage arm causes the electrical resistor to move a second distance toward said first means, said second distance being substantially less than said first distance.

3. Apparatus as defined in claim 2 wherein:

said actuating arm movable a third distance during movement of said first linkage arm said first distance, said actuating arm movable a fourth distance during movement of said second linkage arm said second distance, said fourth distance being greater than said third distance.

4. Apparatus as defined in claim 1 wherein:

said different velocities comprise a first velocity and a second velocity, said first velocity being substantially less than said second velocity, said first velocity occurring when said electrical resistor is located adjacent said first means, said second velocity occurring when said electrical resistor is spaced a substantial distance from said first means. 

1. An electrical resistor trimming apparatus comprising: first means for decreasing the cross sectional area of an electrical resistor; second means for fixedly locating the electrical resistor on a support; third means for moving the electrical resistor into and out of association with said first means, said third means including variable speed structure to move the support and the electrical resistor at different velocities.
 2. An electrical resistor trimming apparatus comprising: first means for decreasing the cross sectional area of an electrical resistor; second means for fixedly locating the electrical resistor on a support; third means for moving the support and the electrical resistor into and out of association with said first means, said third means including variable speed structure; and said variable speed structure includes an actuating arm movable by an actuating force, said actuating arm connected to actuate a first linkage arm and a second linkage arm, said first linkage arm movable with respect to said second linkage arm and causing the electrical resistor to move a first distance toward said first means, said second linkage arm movable subsequent to the completion of movement of said first linkage arm, said second linkage arm causes the electrical resistor to move a second distance toward said first means, said second distance being substantially less than said first distance.
 3. Apparatus as defined in claim 2 wherein: said actuating arm movable a third distance during movement of said first linkage arm said first distance, said actuating arm movable a fourth distance during movement of said second linkage arm said second distance, said fourth distance being greater than said third distance.
 4. Apparatus as defined in claim 1 wherein: said different velocities comprise a first velocity and a second velocity, said first velocity being substantially less than said second velocity, said first velocity occurring when said electrical resistor is located adjacent said first means, said second velocity occurring when said electrical resistor is spaced a substantial distance from said first means. 